This invention relates to display screens, and more particularly, to projection display screens for rear projection displays, front projection displays and tiled projection displays.
The performance and flexibility of projection displays has increased dramatically in recent years. This has produced dramatic growth in the use of projection displays in an ever increasing number of applications. In addition to film based systems, significant advances have been made in the electro-optic technologies for image generation. These technologies include Cathode Ray Tubes (CRTs), Liquid Crystal Displays (LCDs), electromechanical light modulators and numerous other light modulation technologies. To support and complement these advances, screen technology has also advanced.
In its most basic form, a projection display screen may include a light scattering element, or diffuser. The screen may be reflective, in the case of a front projection display, or transmissive in the case of a rear projection display. Numerous variations of light scattering elements have been developed, including volume scatterers, surface scatterers, holographic diffusers, beads, lenticular elements and the like.
While a diffuser can serve the basic function of a projection screen, additional features are often desirable in selected applications. For example, structures that suppress the reflection of ambient light are often incorporated into projection screens. Controlled scattering angles have also been used to maximize the luminance of the viewable light within a range of viewing angles. Uniformity enhancing mechanisms such as Fresnel lenses have also been placed behind or incorporated into the back of rear projection screens.
An illustrative prior art projection system is shown in FIGS. 1A-1B. As shown, a red CRT projector 10, a green CRT projector 11 and a blue CRT projector 12 together project a full color image. The image is focused in the proximity of projection screen 14. Before the light reaches projection screen 14, the light rays are redirected by Fresnel lens 13 to impinge on screen 14 at substantially a normal angle of incidence. As shown in FIG. 1B, screen 14 may be a dual lenticular structure having a rear and front lenticular surface 15 and 16, respectively. The rear lenticular surface 15 approximately focuses the light onto the front lenticular surface 16, in the region between black stripes 18. Black stripes 18 absorb a substantial portion of the incident ambient light, thereby increasing the contrast of the screen. To complete the screen and control the effective scattering profile, diffusers 17 are incorporated into or onto the screen. In the example shown, the additional diffusers determine the degree of scattering in the vertical axis along the direction of the lenslets.
The two lenticular surfaces 15 and 16 function to provide a controlled amount of scatter in the direction normal to the lenticular axes. The lenticular surfaces 15 and 16 may also compensate for the relative offset between the red, green and blue projectors to minimize color shifts as a function of viewing angle.
U.S. Pat. No. 5,434,706 to Matani et al.; U.S. Pat. No. 5,196,960 to Matsuzaki et al.; U.S. Pat. No. 5,457,572 to Ishii et al.; and U.S. Pat. No. 5,724,188 to Kumagai et al. disclose variations on this basic approach. These schemes tend to work well for relatively low resolution applications, such as projection television applications using formats such as NTSC. At higher resolutions, however, the prior art approaches can become obtrusive and can limit the useful resolution of the display. For example, U.S. Pat. No. 5,724,188 to Kumagai et al. discusses some of the difficulties in manufacturing suitable screens for high resolution, including difficulties in making thin screen elements, maintaining rigidity and maintaining contrast.
The difficulties associated with prior art screen technologies, both diffusely scattering and lenticular, become increasingly problematic when the resolution is further increased by providing a number of tiled projectors. In a tiled display, an additional source of non-uniformity is introduced. As illustrated in FIG. 2A, the luminance uniformity of a tiled display is typically a function of viewing angle. More specifically, FIG. 2A shows two non-overlapped projectors 20 and 21 projecting light onto a screen 29. Several resulting scattering profiles 22 through 26 are also shown. Profiles 22 and 26 show how light incident normal to screen 29 is scattered. As the incident light becomes more off-axis, however, profiles such as 23 and 25 result. At the seam, which is the point where the two sets of projected rays meet, a profile such as profile 24 is obtained.
FIG. 2B shows two different observation reference points 27 and 28. From the various profiles, it is clear that the luminance image observed across the screen from reference point 27 is in general different from that observed from reference 28 (i.e. looking at the screen from a different angle). This effect can be reduced by overlapping the images of adjacent projectors, as more fully described in a co-pending U.S. patent application Ser. No. 09/159,340, entitled xe2x80x9cMETHOD AND APPARATUS FOR PROVIDING A SEAMLESS TILED DISPLAYxe2x80x9d, which is incorporated herein by reference. Providing overlap can also aid in other subjective measures of perceived seamlessness, such as color uniformity and vernier mismatch between tiles. Therefore, the ability for a projection screen to support overlap is highly desirable.
Many prior art screens cannot readily support overlap in tiled displays. For example, in a prior art Fresnel field lens approach, little or no overlap is allowed because each projector must typically have a distinct Fresnel lens. The Fresnel lens simply cannot compensate for light emanating from different spaced locations. Because little or no overlap is allowed, the projected image from each projector must typically be precisely matched in size and location with the corresponding Fresnel lens to minimize the visible seams. This greatly impacts the alignment tolerance and stability of the resulting system. Further, it may be difficult to mask slight variations in luminance or color coming from adjacent projectors.
Still further constraints are often placed on high resolution systems. Numerous artifacts such as Moire patterns can result when the screen features interfere with the Fresnel pitch or the projected image pitch. Pixel substructure may be visible in some or all regions of the screen, luminance efficiency may be of high importance and ambient light conditions may be extreme. All of these can lead to significant tradeoffs when working within the framework of prior art screen approaches.
The present invention overcomes many of the disadvantages of the prior art by providing an angle re-distributing prescreen that minimizes or eliminates the screen sensitivity to projector location, in conjunction with a screen preferably having established screen characteristics such as diffusion characteristics. Compatible screen structures are contemplated, along with methods for fabricating the prescreen and maintaining the desired relationship between the prescreen and the screen.
The use of an angle re-distributing prescreen to act as a position-independent field lens combined with a separate screen provides a number of advantages over the prior art. For example, the angle re-distributing nature of the prescreen can de-couple the characteristics related to projector location from other screen characteristics. This allows the screen characteristics to be selected on the basis of ambient light performance, light distribution, or other performance considerations important in the target application. Furthermore, when the prescreen is used with a conventional screen such as a conventional diffusion screen, the cost of the screen assembly may be reduced, and the scalability of the screen may be improved.
In one illustrative embodiment, the display screen includes a lenticular lens array disposed adjacent to an incidence side of a screen, and a diffusion screen disposed adjacent to an emission side of the screen. The diffusion screen may or may not be separated from the lenticular lens array.
To secure the lenticular lens array to the diffusion screen, an edge clamping assembly may be provided. The edge clamping assembly may clamp the edges of the diffusion screen to the lenticular lens array. To maintain a gap between the lenticular lens array and the diffusion screen, one or more edge spacers may be inserted between the lenticular lens array and the diffusion screen. In some embodiments, the edge clamping assembly may apply lateral tension to the lenticular lens array and/or diffusion screen, to provide a more uniform spacing between the lenticular lens array and the diffusion screen.
Rather than using an edge clamping assembly, it is contemplated that the lenticular lens array may be spot bonded to the diffusion screen at predetermined bonding locations. A gap may be maintained, if desired, except at the predetermined bonding locations. It is contemplated that spot bonding may be used in lieu of, or in addition to, the edge clamping assembly discussed above.
Preferably, the lenticular lens array is formed on a first substrate, and the diffusion screen is formed on a second substrate. The first substrate and the second substrate may or may not be separated by a gap. To secure the lenticular lens array to the diffusion screen, a third substrate may be provided. The lenticular lens array may then be sandwiched between the third substrate and the diffusion screen.
The lenticular lens array may also be secured to the diffusion screen using a sealing mechanism. The sealing mechanism may provide a seal around the edges of the lenticular lens array and the diffusion screen, leaving a sealed space therebetween. By applying a negative pressure to the sealed space, the lenticular lens array may be held in place relative to the diffusion screen. Other methods for holding the lenticular lens array in close proximity to the diffusion screen include using an electrostatic force or the like.
It is contemplated that the lenticular lens array may include single or dual sided lenticular lenslets, single or dual sided refractive Fresnel lenslets, Gradient Refractive Index (GRIN) lenslets, holographic lenslets having one or more holographic layers, cylindrical lenslets, or any other type of lenslets. Furthermore, it is contemplated that some of the lenslets in the array of lenslets may be different from others. For example, it is contemplated that the shape and/or size of selected lenslets may be different from the shape and/or size of other lenslets in the array.
As indicated above, the screen assembly of the present invention may be used in conjunction with a tiled projection display. A tiled projection display typically includes two or more projectors, each projecting an image onto a screen. Often, the images of adjacent projectors overlap one another on the incidence side of the screen. The screen assembly of the present invention preferably includes an array of lenslets disposed adjacent to the incidence side of the screen, and a diffusion screen disposed adjacent the emission side of the screen. Configured in this way, the array of lenslets in the prescreen may redirect the incident light from each of the projectors toward the diffusion screen.
In some applications, it may be desirable to restrict the spatial extent of the incoming light to a predetermined range for each lenslet. To accomplish this, an array of light apertures are provided. For example, in one illustrative embodiment, an array of lenslets is provided on one side of a substrate, and an array of light apertures is provided on the opposing side of the substrate. The array of apertures are in registration with the array of lenslets. The apertures function to provide an output which is angularly balanced.
A number of methods for fabricating high resolution display screens are also contemplated. In one illustrative method, a registered dual lenticular prescreen is provided. This method includes the steps of: (1) providing a first roller having a first pattern on a surface thereof for providing a first lenticular pattern on a first side of the prescreen; (2) providing a second roller having a second pattern on a surface thereof for providing a second lenticular pattern on a second side of the prescreen; (3) feeding a deformable material between the first roller and the second roller; (4) turning the first and second rollers in opposite directions to advance the deformable material; and (5) maintaining the registration of the first roller with respect to the second roller so that the first pattern and the second pattern remain in registration with each other.
It is contemplated that the first roller and the second roller may be heated to a predetermined temperature. Preferably, the first roller and the second roller are kept at the predetermined temperature by actively heating and/or cooling the rollers, ideally by using a feedback system. By maintaining a relatively constant temperature, the expansion and contraction of the rollers may be reduced. In one example, the temperature of the rollers may be controlled by providing electric heat, or selectively circulating heated fluid through the rollers. Finally, it is recognized that by only providing a pattern on one of the rollers, a single sided lenticular prescreen may be formed.
Another illustrative method for forming a registered dual lenticular prescreen includes the steps of: (1) providing a first mold having a first pattern on a surface thereof for providing a first lenticular pattern on a first side of the prescreen; (2) providing a second mold having a second pattern on a surface thereof for providing a second lenticular pattern on a second side of the prescreen, wherein the first mold is spaced from the second mold; (3) moving a deformable material into the space between the first mold and the second mold; (4) moving the first mold and the second mold toward one another to emboss or otherwise deform the deformable material with the first pattern on the first side of the prescreen and the second pattern on the second side of the prescreen; (5) moving the first mold and the second mold away from one another; (6) moving the deformable material in a predetermined direction; and (7) moving the first mold and the second mold toward one another to emboss or otherwise deform the deformable material with the first pattern on the first side of the prescreen and the second pattern on the second side of the prescreen.
To align the molds with previously formed lenticular lenslets, it is contemplated that the deformable material may be moved until a previously formed lenslet is detected by a detection system, such as an optical detection system. It is contemplated that the deformable material may be moved in either an X-direction, a Y-direction, or both. Finally, it is recognized that by only providing a pattern in one of the molds, a single sided lenticular prescreen may be formed.
In another illustrative method, an array of optical apertures is formed using an array of preformed lenslets. This method includes the steps of: (1) providing a photosensitive material adjacent the array of lenslets; (2) providing incident light to at least a portion of the array of lenslets, wherein the array of lenslets direct the light toward the photosensitive material; and (3) developing the photosensitive material and removing or otherwise processing selected portions of the photosensitive material to form the array of optical apertures. Preferably, only the photosensitive material that was exposed to light is removed. The photosensitive material may be a photo-resist, a silver-halide emulsion, or any other photosensitive material.